This project is an exploratory study of the efficacy of a new diagnostic method for evaluating the vasculature known as virtual angioscopy (VA). VA is performed by acquiring high-resolution images of the blood vessels of interest, using either computed tomography (CT) or magnetic resonance (MR) images. These images are used to generate a three-dimensional (3D) model of the blood vessel wall on a graphics workstation. The model can be manipulated to allow the viewer to Ofly throughO the blood vessel, providing views similar to those obtained during angioscopy. The technique produces a display of human arterial and venous anatomy in a readily understood format. Moreover, it may allow investigation of vascular stenosis and atherosclerotic plaques. Research in the literature suggests that plaque morphology may be an important determinant of the incidence of stroke and transient ischemic attack. Patients studied in this protocol will have known atherosclerotic plaque in the region of the carotid bulb and will have been referred for carotid endarterectomy. The surgery will be done at Georgetown University Hospital or the National Naval Medical Center, and the imaging will be done in the NIH Clinical Center Department of Radiology. The study design consists of high resolution MR scanning of the neck followed by 3D surface rendering of the carotid arteries. Plaque morphology will be compared to pathologic analysis. We anticipate that VA will yield new insights into plaque morphology. Recent expanded collaborations with NINDS (Dr. T.J. DeGraba) ensure increased patient accrual in the coming months.